Benschop et al. BMC Medicine (2017) 15:153 DOI 10.1186/s12916-017-0917-2
RESEARCH ARTICLE
Open Access
Gestational hypertensive disorders and retinal microvasculature: the Generation R Study Laura Benschop1*, Sarah Schalekamp–Timmermans1, Jeanine E. Roeters van Lennep2, Vincent W. V. Jaddoe3,4, Tien Yin Wong6, Carol Y. Cheung6,7, Eric A. P. Steegers1 and Kamran M. Ikram3,5
Abstract Background: Changes in the microvasculature associated with pre-eclampsia and gestational hypertension have been proposed as a potential pathway in the development of cardiovascular disease. We examined whether gestational hypertensive disorders, such as pre-eclampsia and gestational hypertension, are related to the maternal retinal microvasculature status after pregnancy. Methods: This study is part of an ongoing population-based prospective cohort study. During pregnancy and 6.2 years after the index pregnancy (90% range 5.7–7.4 years), we examined 3391 women with available information on pre-eclampsia, gestational hypertension, and retinal vascular calibers. Retinal arteriolar and venular calibers were measured in the left eye from digitized retinal photographs. Results: Women with pre-eclampsia had smaller retinal arteriolar calibers 6 years after pregnancy than women with a normotensive pregnancy (adjusted difference: –0.40 standard deviation score [SDS]; 95% confidence interval [CI]: –0.62, –0.19). For women with previous gestational hypertension, similar trends were observed (–0.20 SDS; 95% CI: –0.34, –0.05). With respect to retinal venular calibers, we did not observe consistent trends for women with previous pre-eclampsia. However, in women with previous gestational hypertension, we observed larger venular calibers (0.22 SDS; 95% CI: 0.07–0.36) than in women with a previous normotensive pregnancy. The association of gestational hypertensive disorders with retinal vessel calibers was mediated through mean arterial pressure at the time of retinal imaging. Conclusions: Compared to women with a previous normotensive pregnancy, women with pre-eclampsia and gestational hypertension show an altered status of the microvasculature 6 years after the index pregnancy. This is reflected by smaller retinal arteriolar calibers and wider retinal venular calibers. These microvascular changes may possibly contribute to the development of cardiovascular disease in later life. Keywords: Pre-eclampsia, Pregnancy induced hypertension, Microvessels, Post-pregnancy retinal imaging
Background Gestational hypertensive disorders (GHD) (e.g., preeclampsia [PE] and gestational hypertension [GH]) affect 7% of pregnancies today [1, 2]. Both disorders are characterized by new onset of hypertension after 20 weeks of gestation and, in the case of PE, proteinuria. All features of GHD were previously believed to resolve after * Correspondence: [email protected] 1 Department of Obstetrics and Gynecology, Erasmus Medical Center, Wytemaweg 80, PO Box 2040, 3000 CA Rotterdam, the Netherlands Full list of author information is available at the end of the article
delivery. However, results from a large meta-analysis show that women with a history of GHD have a twofold to sevenfold increased risk of developing cardiovascular disease (CVD) in later life [3]. The exact pathophysiologic mechanism underlying this increased CVD risk remains unclear. Nevertheless, it has been shown that microvascular endothelial dysfunction as reflected by a reduced brachial artery flow-mediated dilatation persists in former pre-eclamptic women for many years after their index pregnancy [4]. These data suggest that the microvasculature may have been affected by GHD and
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Benschop et al. BMC Medicine (2017) 15:153
Page 2 of 9
therefore forms an important link between GHD and the development of CVD in later life. In recent years, retinal vascular imaging has emerged as a non-invasive technique to visualize the microvasculature [5–7]. Using this technique in individuals over 50 years of age, several studies have shown that microvascular pathology is an independent contributor to the development of CVD in later life, especially in women [8]. Furthermore, a recent study examining the vasodilatory response of retinal vessels to flicker light showed that women with PE had reduced arteriolar vasodilatation during and after pregnancy compared to women with a normotensive pregnancy, indicating that microvascular dysfunction may already start early in life [9]. Examining the retinal microvasculature may provide further insight into why women with previous GHD have an increased risk for developing CVD later in life. In the current study we investigated the association between a history of GHD and the status of the microvasculature 6 years after the index pregnancy, as reflected by retinal vascular calibers, in women between the ages of 24 to 36 years.
Methods Design and study population
This study was embedded in the Generation R Study, a population-based prospective cohort study from early pregnancy onwards in Rotterdam, the Netherlands [10, 11]. The study has been approved by the Medical Ethics Committee of the Erasmus University Medical Center (Erasmus MC), Rotterdam, the Netherlands, and the procedures followed were in accordance with institutional guidelines [12]. Written informed consent was obtained from all participants. For the present study we included women with a live born singleton with available information on GHD and on postnatal follow-up data. Women were excluded from the main analyses when they had a history of chronic hypertension prior to enrollment in the Generation R Study. We also excluded women who were pregnant during follow-up and women without information on retinal vascular calibers during the follow-up visit 6 years after the index pregnancy. The final population for analysis comprised 3391 women (Fig. 1). Gestational hypertensive disorders
The presence of doctor-diagnosed PE or GH was retrieved from hospital charts and was determined on the basis of the former criteria described by the International Society for the Study of Hypertension in Pregnancy of 2001 [13, 14]. GH was defined by a systolic blood pressure ≥140 mmHg or a diastolic blood pressure ≥90 mmHg after 20 weeks of gestation in previously normotensive women. PE was defined as de novo GH with
Fig. 1 Flowchart of women involved in the study
concurrent new onset proteinuria in a random urine sample with no evidence of urinary tract infection [13]. Maternal blood pressure and anthropometrics
Blood pressure was measured at study enrollment (median 13.2 weeks of gestation [90% range 10.6– 17.0 weeks]) and 6 years after the index pregnancy (90% range, 5.7–7.4 years) as the average of two systolic and diastolic blood pressure readings, with the validated Omron 907 automated digital oscillometric sphygmomanometer (OMRON Healthcare Europe B.V., Hoofddorp, the Netherlands) [15]. All participants were in a standardized supine position to prevent differences due to position. A cuff was placed around the right upper arm. In case of an upper arm exceeding 33 cm, a larger cuff (32–42 cm) was used. The mean value of two blood pressure readings over a 5-min interval was documented for each participant. Blood pressure was measured by trained research assistants wearing normal clothing (i.e., no white coat). Mean arterial pressure (MAP) 6 years after pregnancy was calculated as the average systolic blood pressure plus two times the average diastolic blood pressure, divided by 3. Hypertension 6 years after the index pregnancy was defined by the average of two consecutive blood pressure readings, with systolic blood pressure ≥140 mmHg
Benschop et al. BMC Medicine (2017) 15:153
and/or diastolic blood pressure ≥90 mmHg or the use of antihypertensive medication [16]. Using an alternative cut-off, with systolic blood pressure ≥130 mmHg and/or diastolic blood pressure ≥80 mmHg, did not change the direction of our results but attenuated our results to non-significant levels. At study enrollment maternal height (in centimeters) and weight (in kilograms) without shoes were measured, after which body mass index (BMI) (in kilograms/meter squared) was calculated. Identical measurements were obtained during follow-up 6 years after pregnancy. Prepregnancy BMI was established at enrollment through a questionnaire. Pre-pregnancy weight was highly correlated with the measured early pregnancy weight (Pearson’s correlation coefficient r 0.95 [P < 0.001]) [17]. Retinal vascular caliber assessment
Retinal vascular calibers were assessed by taking digital retinal photographs 6 years after the index pregnancy. Unilateral and unfractionated photographs were taken of the left eye by a Topcon digital retinal camera (model TRC, NW300) while centered on the optic disk. The resolution of the images was set to 4096 and 3072 pixels. Additionally, a semi‐automatic computer‐imaging program was used to measure the six largest retinal arteriolar and venular calibers of the photos. These calibers were located one half to one disk diameter from the optic disk margin [18]. The averages of the six largest retinal arteriolar and retinal venular calibers were then summarized as central retinal arteriolar and central retinal venular equivalents [19]. The semi‐automatic computer‐imaging program that was used for computation of the central retinal arteriolar and central retinal venular equivalents was operated by two graders who were blinded to participants’ characteristics. Grader-specific standard deviation scores (SDSs) were used for both central retinal arteriolar and central retinal venular equivalents. Intraclass correlation coefficients between both graders were excellent for both retinal arteriolar calibers (0.77; 95% confidence interval [CI]: 0.69–0.84) and retinal venular calibers (0.87; 95% CI: 0.81–0.91). This suggests adequate reproducibility. Covariates
Information on maternal characteristics during pregnancy, including maternal age, self-reported pre-pregnancy weight, gravidity, parity, ethnicity, educational level, smoking, and chronic hypertension, was available from questionnaires repeatedly applied during pregnancy. Information on gestational age at birth, birth weight, and child sex was obtained from medical records [20, 21]. Six years after the index pregnancy, we obtained information, through questionnaires, on gravidity and parity at follow-up, medication intake, and smoking.
Page 3 of 9
Statistical analysis
We performed four types of analyses. First, a nonresponse analysis was performed by comparing subject characteristics between mothers with and mothers without available follow-up data 6 years after the index pregnancy (Additional file 1). Women with available follow-up data, but without information on retinal vascular calibers, were left out of the non-response analysis. Second, to reduce the possibility of potential bias associated with missing data, missing values in covariates were imputed using multiple imputation procedures. Five draws for each missing value were performed providing five substituted data points, which in turn created five completed datasets. Analyses were performed separately on each completed dataset and thereafter combined into one global result [22]. In the total population for analysis, 19.4% had missing information on pre-pregnancy BMI, 2.3% on ethnicity, 6.7% on education, 11.3% on smoking during pregnancy, 29.5% on gravidity at followup, 29.9% on smoking during follow-up, 2.3% on blood pressure during follow-up, and 0.2% on medication intake during follow-up. Third, differences in maternal characteristics during pregnancy and follow-up were compared between women with GHD and women with normotensive pregnancies using one-way analysis of variance (ANOVA) for continuous variables and chisquare tests for categorical variables. Fourth, associations between GHD, normotensive pregnancies, and retinal vascular calibers were assessed through linear regression. The linear regression model included covariates selected based on their associations with the outcome of interest based on previous studies or a change in effect estimate of >10% (maternal age at enrollment, ethnicity, educational level at enrollment, smoking during pregnancy, and pre-pregnancy BMI; lastly, when assessing retinal arteriolar caliber, we additionally adjusted for retinal venular caliber and vice versa. GHD are known to increase blood pressure, and blood pressure is known to be associated with smaller retinal arteriolar calibers [23]. To examine the mediating role of mean arterial blood pressure at the time of retinal imaging in the association of GHD with retinal vascular calibers, we analyzed the direct and indirect causal mediation effects through mediation analyses [24]. We used the full model, as was used for linear regression analysis, to adjust for confounding. Statistical analyses were performed using the Statistical Package for the Social Sciences version 21.0 for Windows (SPSS Inc., Chicago, IL, USA) and R version 3.3.2 (R foundation for Statistical Computing, Vienna, Austria [packages ‘foreign’, ‘rms’ and ‘mediation’]) [25].
Results Tables 1 and 2 show maternal characteristics during pregnancy and 6 years after the index pregnancy.
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Table 1 Subject characteristics by gestational hypertensive disorder (n = 3391) P value
Normotensive pregnancy
GH
PE
(n = 3183)
(n = 145)
(n = 63)
Age at enrollment (years)
30.1 (5.1)
30.4 (5.1)
29.4 (5.5)
0.44
Gestational age at enrollment (weeks)
13.9 (10.9, 22.2)
13.4 (10.1, 22.9)
13.8 (10.3, 22.5)
0.15
Height (cm)
166.6 (7.4)
168.0 (7.3)
165.3 (6.8)
0.03
Pre-pregnancy weight (kg)
64.0 (50.0, 87.0)
70.0 (54.0, 114.4)
68.0 (53.2, 105.0)
RESEARCH ARTICLE
Open Access
Gestational hypertensive disorders and retinal microvasculature: the Generation R Study Laura Benschop1*, Sarah Schalekamp–Timmermans1, Jeanine E. Roeters van Lennep2, Vincent W. V. Jaddoe3,4, Tien Yin Wong6, Carol Y. Cheung6,7, Eric A. P. Steegers1 and Kamran M. Ikram3,5
Abstract Background: Changes in the microvasculature associated with pre-eclampsia and gestational hypertension have been proposed as a potential pathway in the development of cardiovascular disease. We examined whether gestational hypertensive disorders, such as pre-eclampsia and gestational hypertension, are related to the maternal retinal microvasculature status after pregnancy. Methods: This study is part of an ongoing population-based prospective cohort study. During pregnancy and 6.2 years after the index pregnancy (90% range 5.7–7.4 years), we examined 3391 women with available information on pre-eclampsia, gestational hypertension, and retinal vascular calibers. Retinal arteriolar and venular calibers were measured in the left eye from digitized retinal photographs. Results: Women with pre-eclampsia had smaller retinal arteriolar calibers 6 years after pregnancy than women with a normotensive pregnancy (adjusted difference: –0.40 standard deviation score [SDS]; 95% confidence interval [CI]: –0.62, –0.19). For women with previous gestational hypertension, similar trends were observed (–0.20 SDS; 95% CI: –0.34, –0.05). With respect to retinal venular calibers, we did not observe consistent trends for women with previous pre-eclampsia. However, in women with previous gestational hypertension, we observed larger venular calibers (0.22 SDS; 95% CI: 0.07–0.36) than in women with a previous normotensive pregnancy. The association of gestational hypertensive disorders with retinal vessel calibers was mediated through mean arterial pressure at the time of retinal imaging. Conclusions: Compared to women with a previous normotensive pregnancy, women with pre-eclampsia and gestational hypertension show an altered status of the microvasculature 6 years after the index pregnancy. This is reflected by smaller retinal arteriolar calibers and wider retinal venular calibers. These microvascular changes may possibly contribute to the development of cardiovascular disease in later life. Keywords: Pre-eclampsia, Pregnancy induced hypertension, Microvessels, Post-pregnancy retinal imaging
Background Gestational hypertensive disorders (GHD) (e.g., preeclampsia [PE] and gestational hypertension [GH]) affect 7% of pregnancies today [1, 2]. Both disorders are characterized by new onset of hypertension after 20 weeks of gestation and, in the case of PE, proteinuria. All features of GHD were previously believed to resolve after * Correspondence: [email protected] 1 Department of Obstetrics and Gynecology, Erasmus Medical Center, Wytemaweg 80, PO Box 2040, 3000 CA Rotterdam, the Netherlands Full list of author information is available at the end of the article
delivery. However, results from a large meta-analysis show that women with a history of GHD have a twofold to sevenfold increased risk of developing cardiovascular disease (CVD) in later life [3]. The exact pathophysiologic mechanism underlying this increased CVD risk remains unclear. Nevertheless, it has been shown that microvascular endothelial dysfunction as reflected by a reduced brachial artery flow-mediated dilatation persists in former pre-eclamptic women for many years after their index pregnancy [4]. These data suggest that the microvasculature may have been affected by GHD and
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Benschop et al. BMC Medicine (2017) 15:153
Page 2 of 9
therefore forms an important link between GHD and the development of CVD in later life. In recent years, retinal vascular imaging has emerged as a non-invasive technique to visualize the microvasculature [5–7]. Using this technique in individuals over 50 years of age, several studies have shown that microvascular pathology is an independent contributor to the development of CVD in later life, especially in women [8]. Furthermore, a recent study examining the vasodilatory response of retinal vessels to flicker light showed that women with PE had reduced arteriolar vasodilatation during and after pregnancy compared to women with a normotensive pregnancy, indicating that microvascular dysfunction may already start early in life [9]. Examining the retinal microvasculature may provide further insight into why women with previous GHD have an increased risk for developing CVD later in life. In the current study we investigated the association between a history of GHD and the status of the microvasculature 6 years after the index pregnancy, as reflected by retinal vascular calibers, in women between the ages of 24 to 36 years.
Methods Design and study population
This study was embedded in the Generation R Study, a population-based prospective cohort study from early pregnancy onwards in Rotterdam, the Netherlands [10, 11]. The study has been approved by the Medical Ethics Committee of the Erasmus University Medical Center (Erasmus MC), Rotterdam, the Netherlands, and the procedures followed were in accordance with institutional guidelines [12]. Written informed consent was obtained from all participants. For the present study we included women with a live born singleton with available information on GHD and on postnatal follow-up data. Women were excluded from the main analyses when they had a history of chronic hypertension prior to enrollment in the Generation R Study. We also excluded women who were pregnant during follow-up and women without information on retinal vascular calibers during the follow-up visit 6 years after the index pregnancy. The final population for analysis comprised 3391 women (Fig. 1). Gestational hypertensive disorders
The presence of doctor-diagnosed PE or GH was retrieved from hospital charts and was determined on the basis of the former criteria described by the International Society for the Study of Hypertension in Pregnancy of 2001 [13, 14]. GH was defined by a systolic blood pressure ≥140 mmHg or a diastolic blood pressure ≥90 mmHg after 20 weeks of gestation in previously normotensive women. PE was defined as de novo GH with
Fig. 1 Flowchart of women involved in the study
concurrent new onset proteinuria in a random urine sample with no evidence of urinary tract infection [13]. Maternal blood pressure and anthropometrics
Blood pressure was measured at study enrollment (median 13.2 weeks of gestation [90% range 10.6– 17.0 weeks]) and 6 years after the index pregnancy (90% range, 5.7–7.4 years) as the average of two systolic and diastolic blood pressure readings, with the validated Omron 907 automated digital oscillometric sphygmomanometer (OMRON Healthcare Europe B.V., Hoofddorp, the Netherlands) [15]. All participants were in a standardized supine position to prevent differences due to position. A cuff was placed around the right upper arm. In case of an upper arm exceeding 33 cm, a larger cuff (32–42 cm) was used. The mean value of two blood pressure readings over a 5-min interval was documented for each participant. Blood pressure was measured by trained research assistants wearing normal clothing (i.e., no white coat). Mean arterial pressure (MAP) 6 years after pregnancy was calculated as the average systolic blood pressure plus two times the average diastolic blood pressure, divided by 3. Hypertension 6 years after the index pregnancy was defined by the average of two consecutive blood pressure readings, with systolic blood pressure ≥140 mmHg
Benschop et al. BMC Medicine (2017) 15:153
and/or diastolic blood pressure ≥90 mmHg or the use of antihypertensive medication [16]. Using an alternative cut-off, with systolic blood pressure ≥130 mmHg and/or diastolic blood pressure ≥80 mmHg, did not change the direction of our results but attenuated our results to non-significant levels. At study enrollment maternal height (in centimeters) and weight (in kilograms) without shoes were measured, after which body mass index (BMI) (in kilograms/meter squared) was calculated. Identical measurements were obtained during follow-up 6 years after pregnancy. Prepregnancy BMI was established at enrollment through a questionnaire. Pre-pregnancy weight was highly correlated with the measured early pregnancy weight (Pearson’s correlation coefficient r 0.95 [P < 0.001]) [17]. Retinal vascular caliber assessment
Retinal vascular calibers were assessed by taking digital retinal photographs 6 years after the index pregnancy. Unilateral and unfractionated photographs were taken of the left eye by a Topcon digital retinal camera (model TRC, NW300) while centered on the optic disk. The resolution of the images was set to 4096 and 3072 pixels. Additionally, a semi‐automatic computer‐imaging program was used to measure the six largest retinal arteriolar and venular calibers of the photos. These calibers were located one half to one disk diameter from the optic disk margin [18]. The averages of the six largest retinal arteriolar and retinal venular calibers were then summarized as central retinal arteriolar and central retinal venular equivalents [19]. The semi‐automatic computer‐imaging program that was used for computation of the central retinal arteriolar and central retinal venular equivalents was operated by two graders who were blinded to participants’ characteristics. Grader-specific standard deviation scores (SDSs) were used for both central retinal arteriolar and central retinal venular equivalents. Intraclass correlation coefficients between both graders were excellent for both retinal arteriolar calibers (0.77; 95% confidence interval [CI]: 0.69–0.84) and retinal venular calibers (0.87; 95% CI: 0.81–0.91). This suggests adequate reproducibility. Covariates
Information on maternal characteristics during pregnancy, including maternal age, self-reported pre-pregnancy weight, gravidity, parity, ethnicity, educational level, smoking, and chronic hypertension, was available from questionnaires repeatedly applied during pregnancy. Information on gestational age at birth, birth weight, and child sex was obtained from medical records [20, 21]. Six years after the index pregnancy, we obtained information, through questionnaires, on gravidity and parity at follow-up, medication intake, and smoking.
Page 3 of 9
Statistical analysis
We performed four types of analyses. First, a nonresponse analysis was performed by comparing subject characteristics between mothers with and mothers without available follow-up data 6 years after the index pregnancy (Additional file 1). Women with available follow-up data, but without information on retinal vascular calibers, were left out of the non-response analysis. Second, to reduce the possibility of potential bias associated with missing data, missing values in covariates were imputed using multiple imputation procedures. Five draws for each missing value were performed providing five substituted data points, which in turn created five completed datasets. Analyses were performed separately on each completed dataset and thereafter combined into one global result [22]. In the total population for analysis, 19.4% had missing information on pre-pregnancy BMI, 2.3% on ethnicity, 6.7% on education, 11.3% on smoking during pregnancy, 29.5% on gravidity at followup, 29.9% on smoking during follow-up, 2.3% on blood pressure during follow-up, and 0.2% on medication intake during follow-up. Third, differences in maternal characteristics during pregnancy and follow-up were compared between women with GHD and women with normotensive pregnancies using one-way analysis of variance (ANOVA) for continuous variables and chisquare tests for categorical variables. Fourth, associations between GHD, normotensive pregnancies, and retinal vascular calibers were assessed through linear regression. The linear regression model included covariates selected based on their associations with the outcome of interest based on previous studies or a change in effect estimate of >10% (maternal age at enrollment, ethnicity, educational level at enrollment, smoking during pregnancy, and pre-pregnancy BMI; lastly, when assessing retinal arteriolar caliber, we additionally adjusted for retinal venular caliber and vice versa. GHD are known to increase blood pressure, and blood pressure is known to be associated with smaller retinal arteriolar calibers [23]. To examine the mediating role of mean arterial blood pressure at the time of retinal imaging in the association of GHD with retinal vascular calibers, we analyzed the direct and indirect causal mediation effects through mediation analyses [24]. We used the full model, as was used for linear regression analysis, to adjust for confounding. Statistical analyses were performed using the Statistical Package for the Social Sciences version 21.0 for Windows (SPSS Inc., Chicago, IL, USA) and R version 3.3.2 (R foundation for Statistical Computing, Vienna, Austria [packages ‘foreign’, ‘rms’ and ‘mediation’]) [25].
Results Tables 1 and 2 show maternal characteristics during pregnancy and 6 years after the index pregnancy.
Benschop et al. BMC Medicine (2017) 15:153
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Table 1 Subject characteristics by gestational hypertensive disorder (n = 3391) P value
Normotensive pregnancy
GH
PE
(n = 3183)
(n = 145)
(n = 63)
Age at enrollment (years)
30.1 (5.1)
30.4 (5.1)
29.4 (5.5)
0.44
Gestational age at enrollment (weeks)
13.9 (10.9, 22.2)
13.4 (10.1, 22.9)
13.8 (10.3, 22.5)
0.15
Height (cm)
166.6 (7.4)
168.0 (7.3)
165.3 (6.8)
0.03
Pre-pregnancy weight (kg)
64.0 (50.0, 87.0)
70.0 (54.0, 114.4)
68.0 (53.2, 105.0)
